Back to EveryPatent.com
United States Patent |
5,534,343
|
Landi
,   et al.
|
July 9, 1996
|
Flexible ballistic resistant article having a thermoplastic elastomeric
honeycomb panel
Abstract
A flexible ballistic resistant article for protecting a user from a high
speed projectile, including an outer layer for stopping the forward motion
of the projectile, and an inner layer disposed between the outer layer and
the user. The inner layer reduces the backface signature of the outer
layer thereby reducing the blunt trauma experienced by the user. The outer
layer including a plurality of plies of high tensile strength fibers. The
inner layer including a honeycomb core formed of undulated strips of
resilient thermoplastic material, thermal compression bonded together to
form cell walls defining a plurality of contiguous regularly shaped cells.
The core having a first face formed by a first extremity of the cell
walls, and a second face formed by a second extremity of the cell walls.
The core further having means for maintaining the core in its expanded
configuration so that it can be used to anisotropically flex to stabilize
and spread the load experienced by the user. The maintaining means being a
facing sheet attached to one of the first and the second faces of the
core. A cover for encasing each of the inner and the outer layers. Means
for attaching the cover to the user.
Inventors:
|
Landi; Curtis L. (Sunnyvale, CA);
Wilson; Susan L. (Sunnyvale, CA);
Huber; Michael S. (Campbell, CA)
|
Assignee:
|
Supracor Systems, Inc. (Sunnyvale, CA)
|
Appl. No.:
|
275771 |
Filed:
|
July 15, 1994 |
Current U.S. Class: |
428/313.5; 2/2.5; 89/36.02; 428/911 |
Intern'l Class: |
F41H 005/02; B32B 003/04; B32B 003/21 |
Field of Search: |
2/2.5
428/911,313.5
89/36.02
|
References Cited
U.S. Patent Documents
2771384 | Nov., 1956 | Collins | 154/52.
|
3337875 | Aug., 1967 | Blakeney | 2/2.
|
3577836 | May., 1971 | Tamura | 2/2.
|
3829899 | Aug., 1974 | Davis.
| |
3894472 | Jul., 1975 | Davis.
| |
3971072 | Jul., 1976 | Armellino.
| |
4004493 | Jan., 1977 | Costanza.
| |
4125053 | Nov., 1978 | Lasker | 89/36.
|
4413357 | Nov., 1983 | Sacks.
| |
4422183 | Dec., 1983 | Landi et al.
| |
4660223 | Apr., 1987 | Fritch.
| |
4681792 | Jul., 1987 | Harpell et al.
| |
5087516 | Feb., 1992 | Groves.
| |
5124195 | Jun., 1992 | Harpell et al.
| |
5187023 | Feb., 1993 | Prevorsek et al.
| |
5196252 | Mar., 1993 | Harpell.
| |
5254383 | Oct., 1993 | Harpell et al.
| |
5317950 | Jun., 1994 | Binon et al. | 2/2.
|
5349893 | Sep., 1994 | Dunn | 89/36.
|
Foreign Patent Documents |
2504849 | Jun., 1975 | DE.
| |
2614892 | Jun., 1976 | DE.
| |
Primary Examiner: Edwards; Newton
Assistant Examiner: Weisberger; Richard C.
Attorney, Agent or Firm: Hamrick; Claude A. S.
Claims
What is claimed is:
1. A flexible ballistic resistant article to protect a user from a high
speed projectile, comprising:
a) an outer layer for stopping the forward motion of said projectile and
including at least one ply having a plurality of fibers;
b) an inner layer for controlling force transmission to said user, said
inner layer being disposed between and adjacent to each of said user and
said outer layer, and including
(i) a honeycomb core formed of undulated strips of resilient thermoplastic
material, thermal compression bonded together to form cell walls defining
a plurality of contiguous regularly shaped cells, said core having a first
face formed by a first extremity of said cell walls and a second face
formed by a second extremity of said cell walls;
(ii) at least one facing sheet of resilient thermoplastic material being
fixably engaged to at least one of said first or second faces to maintain
said core in an expanded configuration so that it can anisotropically flex
to stabilize and spread the load when said article is impacted by the
projectile;
c) a cover for encasing each of said inner and said outer layers; and
d) a user attachment means for being engaged to said cover for removably
attaching said cover to said user.
2. A flexible ballistic resistant article as recited in claim 1, wherein at
least one of said first and second faces of said core is non-planar.
3. A flexible ballistic resistant article as recited in claim 2, wherein
said core includes perforations formed in at least one of said cells
walls.
4. A flexible ballistic resistant article as recited in claim 3, wherein
said
facing sheet of resilient thermoplastic material is thermal compression
bonded to said first face of said core.
5. A flexible ballistic resistant article as recited in claim 1, wherein
said outer layer includes:
a) a first material layer having at least one ply of unidirectional layers
of high strength fibers; and
b) a second material layer having a plurality of interwoven fibers of high
strength.
6. A flexible ballistic resistant article as recited in claim 5, wherein at
least one of said first and second faces of said core is non-planar.
7. A flexible ballistic resistant article as recited in claim 6, wherein
said core includes perforations formed in at least one of said cells
walls.
8. A flexible ballistic resistant article as recited in claim 7, wherein
said
facing sheet of resilient thermoplastic material is thermal compression
bonded to said first face of said core.
9. A flexible ballistic resistant article as recited in claim 1, further
including:
a) an inner material layer having at least one ply of high strength fibers,
and being disposed adjacent to and between each of said user and said
inner layer.
10. A flexible ballistic resistant article as recited in claim 9, wherein
at least one of said first and second faces of said core is non-planar.
11. A flexible ballistic resistant article as recited in claim 10, wherein
said core includes perforations formed in at least one of said cells
walls.
12. A flexible ballistic resistant article as recited in claim 11, wherein
said facing sheet of resilient thermoplastic material is thermal
compression bonded to said first face.
Description
BACKGROUND TO THE INVENTION
1. Field of the Invention
The invention relates to a flexible ballistic resistant article of the type
which can be worn to protect the wearer from a high speed projectile such
as a bullet fired from a handgun or a rifle. More particularly, the
present invention relates to an improved flexible ballistic resistant
article having a thermoplastic elastomeric honeycomb panel disposed
therein.
2. Description of the Prior Art
Personal use ballistic resistant shields, e.g., body armor, having a rigid
construction are known. For example, in a common type of shield, the
material used in an outer bullet-trapping layer essentially includes an
array of metallic plates joined by tough flexible cloth to provide a
wearable garment. These shields can provide effective protection but are
uncomfortable to wear because of their bulk, weight, stiffness, and lack
of breathability. Illustrative of bullet-proof shields having metallic
plates or sheets disposed within are described in U.S. Pat. Nos.
5,187,023, 4,660,223, 4,004,493, 3,971,072, 3,894,472 and 3,829,899.
Also known are ballistic resistant shields which include high tensile
strength penetration-resistant fabrics that are somewhat flexible. Fibers
used in such articles include aramid fibers, graphite fibers, nylon
fibers, ceramic fibers, polyethylene fibers, glass fibers and the like.
For many applications, such as vests or parts of vests, the fibers are
used in a woven or knitted fabric, and encapsulated or embedded in a
matrix material. However, in body shields made from materials such as
these, it is difficult to limit the risk of serious injury to the user
while at the same time designing a shield having low weight, reduced bulk
and appreciable flexibility. This is because the fibers of the
penetration-resistant fabric stretch as they absorb a bullet's energy
thereby creating a bulge at a back surface of the shield, i.e. a surface
opposite the surface of the shield impacted by the bullet. The bulge at
the back surface can transmit an appreciable shock to an adjacent region
of the user's body. The bulge at the back surface of the shield, is
referred to as the "backface signature", and the transmitted shock is
called the "blunt trauma" experienced by the shield user.
U.S. Pat. No. 4,413,357 discloses a protective shield having an outer
penetration-resisting layer comprised of at least eight and preferably
twenty-eight individual superposed plies of close woven fabric of aramid
fibers, an intermediate impact-spreading layer comprised of at least one
ply of thin flexible impervious plastic sheet such as polycarbonate, and
an inner or impact-cushioning layer formed from relatively soft and thick
foam plastic that absorbs the impact and bullet bulge of the polycarbonate
sheet.
U.S. Pat. No. 5,087,516 discloses body armor having an outer component and
an inner component. The outer component, flattens and traps a striking
bullet, while the inner component spreads the impact of the bullet. The
outer component includes a pair of layers of flexible material at least
the inner layer of which is high impact-resistant material having at least
two juxtaposed inter-nested layers of hard glass beads between the
flexible layers, each layer of glass beads being arranged in a close
packed lattice pattern.
U.S. Pat. No. 5,196,252 discloses a ballistic resistant body armor
comprising a substrate layer having a plurality of planar, non-metallic
bodies mechanically affixed to a surface thereof.
A disadvantage associated with each of the articles disclosed is that a
critical component of each is a relatively rigid plate or item, e.g.
polycarbonate sheet, non-metallic bodies, or glass beads, thereby
rendering the entire ballistic shield stiff, inflexible, heavy and
generally uncomfortable to use.
U.S. Pat. No. 4,422,183 discloses a protective body shield including a
honeycomb core arranged with the axis of each cell of the honeycomb panel
aligned perpendicular to the body surface of the wearer. A layer of
resilient foam covers at least the one side of the shield that is in
contact with the body to produce a shield that is rigid and shock
absorbing in the direction of anticipated impacts, but flexible and
yieldable in other directions so as not to interfere with the movement of
the wearer's body. It is clear from the disclosure that the protective
body shield is not made from ballistic resistant materials and therefore
unsuitable for use as a ballistic resistant article.
Thus, there is a need for a ballistic resistant article that overcomes the
deficiencies of the prior art devices.
SUMMARY OF THE INVENTION
Objects of this Invention
It is an object of the present invention to provide an improved flexible
ballistic resistant article.
It is another object of the present invention to provide an improved
flexible ballistic resistant article having flexible fibers and a
thermoplastic elastomeric honeycomb panel.
It is another object of the present invention to provide an improved
flexible ballistic resistant article having a reduced backface signature,
as compared to other non-metallic ballistic resistant articles, thereby
reducing the amount of blunt trauma experienced by a user of the article.
It is yet another object of the present invention to provide an improved
flexible ballistic resistant article that is light in weight.
It is still another object of the present invention to provide an improved
flexible ballistic resistant article that is flexible and somewhat
breathable, and generally comfortable to wear.
Briefly, a flexible ballistic resistant article for protecting a user from
a high speed projectile, includes an outer layer for stopping the forward
motion of the projectile, and an inner layer disposed between the outer
layer and the user. The inner layer reduces the backface signature of the
outer layer thereby reducing the blunt trauma experienced by the user. The
outer layer including at least one ply of high tensile strength fibers.
The inner layer including a honeycomb core formed of undulated strips of
resilient thermoplastic material, thermal compression bonded together to
form cell walls defining a plurality of contiguous regularly shaped cells.
The core having a first face formed by a first extremity of the cell
walls, and a second face formed by a second extremity of the cell walls.
The core further having means for maintaining the core in its expanded
configuration so that it can be used to anisotropically flex to stabilize
and spread the load experienced by the user. A cover for encasing each of
the inner and the outer layers. Means for attaching the cover to the user.
An advantage of the present invention is that it provides a ballistic
resistant article that reduces the backface signature of the projectile
stopping substrate layer.
Another advantage of the present invention is that it provides a ballistic
resistant article that reduces the blunt trauma experienced by a user of
the article.
Another advantage of the present invention is that it provides a ballistic
resistant article that is constructed from materials having improved
flexibility and shock absorption capability.
Still another advantage of the present invention is that it provides a
ballistic resistant article that is lightweight and comfortable to wear.
Another advantage of the present invention is that since the projectile
stopping substrate is used to stop the projectile and not to reduce the
backface signature the number of plies of the projectile stopping
substrate can be reduced.
These and other objects and advantages of the present invention will no
doubt become apparent to those skilled in the art after having read the
following detailed description of the preferred embodiment which is
contained in and illustrated by the various drawing figures.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing:
FIG. 1 is a side view schematically depicting the inner components of one
embodiment of the present invention attached to a user;
FIG. 2 is a perspective view showing a preferred embodiment of the present
invention having succeeding layers of material removed to reveal a
flexible thermoplastic elastomeric honeycomb panel;
FIG. 3 is a cross sectional view, illustrating another alternate embodiment
of the present invention;
FIG. 4 is a cross sectional view, illustrating yet another alternate
embodiment of the present invention;
FIG. 5 is a cross sectional view, depicting still another alternate
embodiment of the present invention;
FIG. 6 illustrates an idealized square-wave force-deflection curve;
FIG. 7a depicts a force-deflection curve of a representative panel of
flexible thermoplastic elastomeric honeycomb of the present invention;
FIG. 7b shows several force-deflection curves representing different
resistant systems, e.g. a coil spring system, an open-cell foam system,
and a system having a flexible thermoplastic elastomeric honeycomb panel;
FIG. 8 depicts a schematic illustration depicting a ballistic test setup as
specified in the National Institute of Justice (NIJ) Standard 0101.03,
entitled "Ballistic Resistance of Police Body Armor"; and
FIG. 9 illustrates several force-deflection characteristic curves comparing
the different panel materials that are used in the ballistic resistant
articles illustrated in FIG. 3-4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a side view schematically illustrating a ballistic-resistant
article 12 worn by a user 10. It should be noted that although an article
12 in the form of a vest is schematically depicted, other articles are
contemplated by the embodiments of the present invention. For example,
helmet liners, screens, back and side body shields, etc. can be fabricated
using the embodiments of the present invention. It should further be noted
the article 12 is attached to the user 10 by attaching means 11 that are
known in the art, e.g. straps, belts, etc.
The article 12 includes a cover or casing 14 which encases an outer layer
16 and an inner layer 18. The casing 14 is made from readily available
fabric materials that are preferably permeable. The casing 14 is shown in
dashed lines in order to more clearly illustrate the layers 16 and 18 of
the article 12. The inner layer 18 is disposed adjacent to and between
each of the user 10 and the outer substrate 16. The inner layer 18 may be
attached, via adhesive or thermal bonding, to the outer layer 16.
Alternately, the layers 16 and 18 may be disposed proximate each other but
unattached to each other.
The outer layer 16 initially engages a high speed projectile (i.e. a
bullet) and stops its forward motion. The layer 16 includes at least one
ply having a plurality of high tensile strength fibers arranged in either
a unidirectional or a woven configuration. It will be appreciated that a
variety of materials, ply and fiber arrangements may be used to construct
the layer 16.
In the specimens tested in the setup illustrated in FIG. 8 and, described
in greater detail below, the layer 16 includes at least one layer of
Spectra.RTM. Shield material (FIG. 1), and several plies of Spectra.RTM.
Fabric material (FIG. 1).
Spectra.RTM. Fabric material is interwoven from high tensile strength
fibers, designated by the trademark Spectra.RTM., which are made from
ultra-high weight polyethylene molecules modified by a special process
patented by Allied-Signal. The Spectra.RTM. fibers can be woven in a
variety of weaves depending on the particular application. Typically in a
ballistics application, a very tight weave would be used.
Spectra.RTM. Shield material is another type of fabric having a plurality
of woven high tensile strength fibers. Because of the warp and weave
interlacing created by the weaving process, the woven fibers (of, for
example, a Spectra.RTM. Fabric material) do not immediately go taught when
the fabric is struck by a bullet. This can be undesirable, as a primary
reason to use Spectra.RTM. fiber (or any other high tensile strength
fiber) in a ballistic resistant article is to take advantage of the
enormous tensile strength of the fiber which is typically ten times
stronger than steel on a weight basis. Consequently, a Spectra.RTM. Shield
layer is made up of two unidirectional sublayers of Spectra.RTM. fibers
held in place with flexible resins, which is sealed between two thin
sheets of polyethylene film. The result is a thin, flexible material
which, when impacted by a high velocity projectile, efficiently loads the
high tensile strength fibers.
Although Spectra.RTM. fibers have been used in the tested specimens, the
preferred embodiment of the present invention can use other types of
similar high tensile strength fibers. For example, high tensile strength
fibers made from other materials, e.g. Kevlar.RTM., may be used to
fabricate the outer layer 16. Also, although an outer layer 16 including
Spectra.RTM. Shield and Spectra.RTM. Fabric materials has been described,
it will be appreciated that alternate material combinations may be used.
The inner layer 18 absorbs energy remaining in the projectile after its
forward motion is stopped by the outer layer 16. The inner layer 18
controls the amount of force transmitted to the user 10 by reducing the
backface signature of the back face 15 of the outer layer 18 and by
mitigating the blunt trauma experienced by the user 10.
FIG. 2 is a perspective view of a preferred embodiment of the present
invention. A ballistic resistant article 20, generally similar to the
article 12 (FIG. 1) is depicted with its casing omitted for clarity
purposes. An outer layer 22 includes a Spectra Shield.RTM. material layer
24 and a Spectra.RTM. Fabric material layer 26. The material layers 24,
and 26 have been cut back to reveal the inner layer 28. The layer 28
includes a honeycomb core 30 which is initially made from a stack of
strips or ribbons 32 and 33 of a selected grade of thermoplastic
elastomeric material. In the preferred embodiment the ribbons are not
perforated, as shown by ribbon 33. However, it will be appreciated that,
in alternate embodiments some or perhaps all of the ribbons may be
perforated such that a matrix of small holes 34 exists throughout, as
illustrated by ribbon 32. The ribbons 32 and 33 are thermal compression
bonded together at spaced intervals staggered between alternate strips, as
depicted at bond joints 36. When the bonded stack is expanded, this
pattern of bonding results in a honeycomb of generally hexagonally or
rectangularly shaped cells 38 (depending on the degree of expansion). The
core 30 manufacturing and fabrication is described in greater detail in
U.S. Pat. No. 5,039,567 which is incorporated herein by reference.
Each cell 38 of the honeycomb core 30 is defined by four generally S-shaped
wall segments 40a-d, each of which is shared by an adjacent cell. As
depicted, each wall segment 40(a-d) of each cell 38 includes a single
thickness wall portion 42 and a double thickness wall portion 44
(including the bond joint 36).
Each wall segment 40 has an outer extremity 46 and an inner extremity 48.
The core 30 has an outer "face" 50 and an inner "face" 52 either or both
of which may be deformed during a planarization operation, as disclosed in
the above-identified U.S. Pat. No. 5,039,567, to form a means for
maintaining the core 30 in its expanded configuration and preventing the
expanded strip stack from collapsing. The inner face 52 is formed
proximate to the inner extremity 48, the outer face 50 is formed proximate
to the outer extremity 46.
A facing sheet 54 is thermal compression bonded to the outer face 50 formed
by the outer extremity 46 of each wall segment 40(a-d). Typically, the
facing sheet 54 would be made from the same material as the core 30, and
can be either perforated or solid. The facing sheet 54 when supported by
the outer extremity 46 of each wall segment 40 has a "trampoline" effect
that mitigates backface signatures of portions of the outer layer 22 that
impinge into the open areas of a cell. That is, the facing sheet 54 covers
an open area of each cell and limits the encroachment of a deformed layer
22 into these open areas.
Although the casing 14 (FIG. 1) separates the inner face 52 of the core 30
from the skin of the user, the magnitude of the projectile velocity is
sufficient to imprint a non-planarized sharp edged inner face 52 onto the
skin of the user. Thus, it is preferable to planarize the inner face in
order to mitigate this "cookie cutter effect."
An important aspect of the present invention is using a flexible
thermoplastic elastomeric honeycomb panel with the outer layer having a
plurality of plies of high tensile strength fibers. A honeycomb panel
absorbs the energy remaining after the high tensile strength fibers of the
outer layer stop the projectile. The use of a honeycomb panel of the
present invention permits fewer plies of ballistic material (i.e. high
tensile strength fiber) to be used in the outer layer to achieve the same
results as shields in the prior art. Thus, shields using a honeycomb panel
of the present invention will be generally lighter, more flexible and more
comfortable to wear without reducing the shield's bullet stopping and
blunt trauma mitigating capability.
The honeycomb core 30 is tear-resistant, highly resilient, yet extremely
light weight. The core 30 (without facing sheets) is approximately 90
percent air, and is lighter than the foams normally used in prior art
ballistic resistant articles.
Another important quality of the core 30 is that it is an anisotropic
three-dimensional structure which has varying degrees of flex in its width
(X), length (Y), and its thickness (Z) dimensions.
Selected combinations of elastomer material and modulus, honeycomb cell
configuration, and core thickness variables will determine the core's 30
softness or hardness, damping characteristics, and rigidity or flex as
required for a particular application. Additionally, by selection and
combination of the ribbons 32, 33 of material that make up the core 30, or
by varying the core 30 dimensions and cell 38 sizes, the flexibility of
the resulting core 30 can be predetermined. For example, the core 30 can
be made to have a greater stiffness (and lesser flexibility) along the
outer area and a lesser stiffness (and greater flexibility) toward the
inner area of the panel or vice-a-versa.
The facing and ribbon materials can be selected from a wide variety of
films, including blends such as urethane/polycarbonates, spun-bonded
thermoplastics such as polyethylene or polypropylene polyester,
thermoplastic urethanes, elastomeric or rubber materials, elastomer
impregnated fibers and various fabrics, etc., or combinations thereof.
FIG. 3 illustrates another embodiment of the present invention. A ballistic
resistant article 56 includes an outer layer 58, an inner layer 59, and an
inner material layer 60. All the layers 58, 59, 60 are encased within a
permeable fabric casing 62. The casings 60 and 14 (FIG. 1), the layers 58
and 22 (FIG. 2), and the layers 59 and 28 (FIG. 2) are generally similar.
It will be appreciated that the core 30 of the layer 59 could have
perforations 34 formed in some or all of the cell walls, as illustrated at
the bottom half of the figure. Alternately, none of the cell walls could
be formed with perforations. As with the article 20 (FIG. 2), the facing
sheet 54 may be either solid or perforated, and fabricated from a gauge of
resilient thermoplastic material that is generally similar to the material
used in the ribbons of the core 30. The facing sheet 54 may be thermal
compression bonded to either the outer face of the core 30, as
illustrated, or bonded to the inner face of the core 30.
The inner material layer 60 is made from a woven high tensile strength
fabrics (e.g. Spectra.RTM. Shield), and disposed between the user and the
core 30. The material layers 24 and 26 are typically bonded to each other,
although they need not be. Similarly, the face sheet 54 may be bonded to
the material layer 26, and the core 30 may be bonded to the material layer
60, although it is not required.
FIG. 4 illustrates another alternate embodiment of the present invention. A
ballistic resistant article 64 having an outer layer 58, an inner layer
66, and an inner material layer 60 encased within a permeable casing 60.
The article 64 is generally similar to the article 56 (FIG. 3) except that
the inner layer 66 does not include a facing sheet. The inner layer 66
includes the flexible thermoplastic elastomeric core 30 which is bare or
unfaced and further having perforations 34 formed in the cell walls
thereof.
FIG. 5 illustrates yet another alternate embodiment of the present
invention. In this embodiment, a ballistic resistant article 68 includes
generally the same elements as the article 64, however the cell walls of
the core 30 do not have perforations formed therein.
In the articles 64 and 68, (FIGS. 4, 5) the honeycomb core 30 was not
bonded to the material layer 26 or the material layer 60. The honeycomb
core 30 is edge-stitched into the fabric casing 62 during the fabrication
of the article. Typically the material layers 24 and 26 are bonded
together, however, it is not required to have these layers attached.
The perforations formed in the cell walls of an article, (e.g. the article
64, FIG. 4) provide several important benefits. The perforations enhance
air flow and moisture transport through the honeycomb cells. This improves
the comfort and wearability and the ballistic resistance characteristics
of the vest. From a comfort standpoint, movement of the wearer flexes the
cells creating an air exchange pumping action through the perforations.
Also, the additional air flow provided by these perforations helps to
minimize the force contribution of the air trapped in the cells compressed
by the backface bulges of the vest when impacted by a projectile.
The ballistics tests for backface signature, to be described in greater
detail below, utilized only sample articles having bare faced honeycomb
panels, i.e only the ballistics resistant articles 64 and 68 (FIG. 4, 5)
were tested. It will be appreciated, however, that the article 56 (FIG. 3)
or the article 20 (FIG. 2) could be tested and would yield similar or
better ballistic test results regarding backface signature.
The flexible, elastomeric honeycomb panel works well in an impact
application because it approaches a "ramp-plateau" or "square wave"
response. These principals are illustrated in FIGS. 6, 7a, and 7b.
In designing a ballistic resistant article it is important to identify a
reasonable maximum force that can be transmitted to the body of the user,
and then design an impact absorbing system that limits the force to this
maximum.
For example, if a reasonable maximum force that can be transmitted to a
body is assumed to be 80 psi, then the most efficient absorption system
would immediately "ramp" up to 80 psi when compressed, or loaded, however
the force transmitted to the user's body would not exceed 80 psi until the
absorption system "bottomed out". In addition, the absorption system
should be designed to absorb the energy before bottoming out. The
absorption system "bottoms out" when it is compressed to such a state
that, in the case of a honeycomb core the cell walls have "accordioned" or
buckled into a solid stack, and no further energy absorption occurs, i.e.
the impacting force is transmitted through the absorption system and
directly to the user with no attenuation whatsoever.
The energy required to compress an isolation or suspension material is
defined as the area beneath a force-deflection plot. This area also
determines the maximum energy that can be absorbed by an isolation or
suspension system. In FIG. 6 an idealized square-wave force-deflection
plot is illustrated. Deflection of the isolation or absorption material is
plotted along the horizontal axis, the amount of force transmitted to the
body of the user is plotted along the vertical axis. It should be noted
that the offset 70 from the vertical axis is only for purposes of
illustrating the response of an ideal isolation or absorption system. An
idealized square-wave 72 has its desired maximum force plateau set at the
maximum force of 80 psi. It will be noted that, in this ideal system, a
force of 80 psi is reached virtually instantaneously. That is, the force
of 80 psi is encountered with no deflection of the isolation material. The
force of 80 psi is maintained for a deflection range of approximately zero
to 70 percent until a bottoming-out region 74 is encountered whereupon the
impact force is transmitted directly to wearer because the isolation or
absorption system has been fully compressed. Increasing the stiffness or
thickness of the panel will increase the energy that can be described.
FIG. 7a illustrates a force-deflection plot for a representative sample of
thermoplastic elastomeric honeycomb material of the present invention. A
force-deflection curve 76 for a flexible thermoplastic elastomeric
honeycomb panel is shown in comparison with the idealized square-wave
response 72 (shown in dashed lines). It will be appreciated that, in a
first portion 78, the curve 76 nearly instantaneously ramps up to the
maximum desired force level plateau of 80 psi. The curve 76, in a second
portion 79, continues to approach the force plateau of 80 psi until the
bottoming-out region 74 is reached at roughly the 70% deflection point. It
is appreciated that the curve 76 is a close approximation of the idealized
square-wave response curve 72 (shown in dashed lines).
FIG. 7b illustrates force-deflection curve comparisons for different
absorption or isolation systems. Specifically, a coil spring system (curve
80), a closed cell foam system (curve 81), and a thermoplastic elastomeric
honeycomb panel system of the present invention (curve 76) are compared to
the ideal square-wave response 72. It is quite evident that for a given
amount of deflection, the area 82 under the curve 76 is much greater than
a corresponding area 83 under the curve 80 representing a linear rate
system (i.e. coil spring) or the area 84 under the curve 81 representing a
rising rate system (i.e. closed cell foam). Assuming that the honeycomb
system has enough area 82 under the curve 76 to absorb the remaining
energy of the bullet without bottoming out, the maximum load that will be
experienced by the user is 80 psi which, in this example, will not cause
blunt trauma. Note that for a rising rate system (i.e. closed cell foam)
to achieve the same result, the thickness of the foam must increase in
order to absorb the same amount of energy. In a linear ramp system as
represented by the curve 80, the thickness required to manage a given
amount of energy is nearly twice that of a honeycomb system, i.e. the
curve 76, since the area 83 beneath the curve 76 is nearly one-half that
of the area 82.
Other energy absorbing systems do not fare as well as honeycomb because
they are either too soft or too thin to absorb the remaining bullet
energy, or are too rigid to be comfortable to wear. As these systems
bottom out they pass energy into the body (or in the case of a ballistics
test, into a clay backing material which records the backface
deformation).
Four different panel configurations were tested using a ballistic test
setup 86 illustrated in FIG. 8. The test setup and procedure is further
described in the National Institute of Justice (NIJ) Standard 0101.03
entitled "Ballistic Resistance Police Body Armor" which is hereby
incorporated by reference. The ballistic test setup 86 includes a test
weapon 88, a start trigger 89, a stop trigger 90 and a test target 92
mounted to a clay backing material 93. The clay material 93 used to back
up the target 92, is considered to be a reasonable approximation of the
user's body resistance. The test weapon 88 is aimed along a line of sight
94 to the vest target 92. The start trigger is in electrical communication
with a chronograph 95 via a wire 96. Similarly, the stop trigger 90 is in
electronic communication with the chronograph 95 via a wire 97. The
operation of the ballistic test is done in accordance with the procedures
as set forth in the NIJ standard 0101.03. The distances A, B, and C,
illustrated in FIG. 8 are described in greater detail in the NIJ standard.
Four sample articles were tested for backface signature using the setup 86
illustrated in FIG. 8. Sample article 1 is substantially identical to
article 64 (FIG. 4). Each of the layers 24, 60 includes one ply of
Spectra.RTM. Shield material. The layer 26 includes 50 plies of
Spectra.RTM. Fabric material. The layer 66 includes a single ply or panel
of honeycomb core 30, fabricated from a SEPP material, which is an
elastomer polypropylene. The ribbon thickness is 10 mil, the cell size is
0.187 inch, and the core thickness is 0.250 inch. The core is not faced,
i.e. bare core, and has perforated cell walls. Sample article 1,
therefore, has a total of 53 plies.
Sample article 2 is substantially identical to the article 68 (FIG. 5).
Each layer 24, 60 includes one ply of Spectra.RTM. Shield material. The
layer 26 includes 50 plies of Spectra.RTM. Fabric material. The layer 69
includes one ply or panel of honeycomb core 30 made from SU90 material, a
urethane having a 90 durometer. The ribbon thickness is 15 mil, the cell
size is 0.187 inch, and the core thickness is 0.250 inch. The core is not
faced and has non-perforated cell walls. Sample article 2 has a total of
53 plies or panels.
Sample article 3 is generally the same configuration as Sample article 2
except that the layer 26 includes 45 plies of Spectra.RTM. Fabric
material. Thus, there are a total of 48 plies and panels. Sample article 4
is generally the same configuration as Sample article 1 except that the
layer 26 includes 45 plies of Spectra.RTM. Fabric material. Thus, there
are a total of 48 plies and panels.
The results for backface signature for the four sample articles are shown
in Table 1. It is significant, that the typical backface signature, i.e.
deformation, when testing any of the sample article configurations is on
the order of 23-24 mm. It should be noted that typical foam backed
ballistic resistant panels have a deformation of 27-32 mm. Further, the
NIJ requires that the deformation for the tested article be less than 44
mm in order to earn a certificate of compliance. The sample articles
exhibited deformations 25-30% lower than the results achieved with a
typical foam liner and about 55% lower than the certification requirements
specified by the NIJ standard. This represents a significant improvement
over the prior art ballistic resistant vests.
FIG. 9 illustrates the force-deflection characteristics of SEPP and SU90
thermoplastic elastomeric honeycomb panels. There is little difference in
the force-deflection characteristics of the SEPP material used in Sample
articles 1 and 4, and the SU90 material used in Sample articles 2 and 3.
Curves 98-101 represent the force-deflection characteristics of two
different honeycomb materials obtained during several force-deflection
measurement tests. Curves 98 and 100 (i.e. the square symbols) illustrate
the SU90 material used in Sample articles 2 and 3, and curves 99 and 101
(i.e. the circle symbols) depict the SEPP material used in Sample articles
1 and 4.
The upper curves 98 and 99 show the resistance to loading exhibited by the
SEPP and SU90 materials. The lower curves 100 and 101 illustrate the
response of the SEPP and SU90 materials when they are unloaded. That is,
the lower curves depict how the materials spring back when the loading is
removed. The area bounded between the upper curves and the lower curves
for the same material (i.e. curves 98, 100 for SU90 material, and curves
99, 101 for SEPP material) is called a hysteresis loop, and shows the
amount of energy absorbed by the specimen during the test. Typically, the
test samples were compressed at 35 inches/sec and uncompressed at 2
inches/min. Thus, the curves 98-101 were not obtained at velocities
comparable to ballistic projectiles. However the general characteristics
should remain the same.
Generally speaking, increasing the ribbon thickness while maintaining a
constant cell size does make the honeycomb panel stiffer in compression.
However, the SU90 material (sample articles 2, 3) is a urethane material,
whereas the SEPP material (sample articles 1, 4) is an elastomeric
polypropylene, which has a higher flexural modulus and is stiffer than
urethane. Consequently, the SEPP material does not require the same ribbon
thickness to achieve the same compressive resistance. Although the
force-deflection performance is similar, the SEPP material is considerably
lighter, and consequently is favored for use as the core material in the
preferred embodiment (FIG. 2). In addition, the SEPP material has more
inherent hysteresis, i.e. greater damping, which means that it internally
absorbs, or dissipates, more energy when struck. The SU90 urethane is more
resilient, and will take more repeated impacts, but that is not the most
important characteristic for this particular application.
Although preferred and alternate embodiments and applications of the
present invention have been disclosed above, it will be appreciated that
numerous applications, alterations
TABLE 1
______________________________________
BALLISTICS TEST RESULTS
Trials
Sample Backface Signature, i.e. deformation (mm)
Article 1 2 3 4 5 6
______________________________________
1 23 21 24 17 18 18
2 22 21 21 14 13 23
3 22 24 23 20 20 22
4 21 21 21 20 21 24
______________________________________
and modifications thereof will no doubt become apparent to those skilled in
the art after having read the above disclosures. It is therefore intended
that the following claims may be interpreted as covering all such
applications, alterations and modifications as fall within the true spirit
and scope of the invention.
Top